Re: [JGIT PATCH 2/2] Decrease the fetch pack client buffer to the lower minimum
From: Junio C Hamano <hidden>
Date: 2016-06-15 22:46:44
"Shawn O. Pearce" [off-list ref] writes:
This is the lowest buffer size we actually require to keep the client and server sides from deadlocking against each other.
Is this about the fetch-pack protocol where
(1) upload-pack shows what it has; fetch-pack keeps reading until it sees
a flush; then
(2) fetch-pack shows what it wants; upload-pack keeps reading; then
(3) fetch-pack sends a bunch of have's, followed by a flush; upload-pack
keeps reading and then responds with an ACK-continue or NAK, which
fetch-pack reads; this step continues zero or more times; and then
finally
(4) fetch-pack sends a bunch of have's, followed by a flush; upload-pack
keeps reading and then responds with an ACK, fetch-pack says done.
Where do you need "enough buffer"? The conversation looks very much "it's
my turn to talk", "now it's your turn to talk and I'll wait until I hear
from you", to me. I am puzzled.
quoted hunk
Also added documentation, and renamed the symbol to better match its real purpose; naming the lower threshold we can allow for a buffer. Signed-off-by: Shawn O. Pearce <redacted> --- .../jgit/transport/BasePackFetchConnection.java | 10 +++++++++- .../org/spearce/jgit/transport/TransportLocal.java | 2 +- 2 files changed, 10 insertions(+), 2 deletions(-)diff --git a/org.spearce.jgit/src/org/spearce/jgit/transport/BasePackFetchConnection.java b/org.spearce.jgit/src/org/spearce/jgit/transport/BasePackFetchConnection.java index eaa94bd..1d1b801 100644 --- a/org.spearce.jgit/src/org/spearce/jgit/transport/BasePackFetchConnection.java +++ b/org.spearce.jgit/src/org/spearce/jgit/transport/BasePackFetchConnection.java@@ -89,7 +89,15 @@ */ private static final int MAX_HAVES = 256; - protected static final int MAX_CLIENT_BUFFER = MAX_HAVES * 46 + 1024; + /** + * Amount of data the client sends before starting to read. + * <p> + * Any output stream given to the client must be able to buffer this many + * bytes before the client will stop writing and start reading from the + * input stream. If the output stream blocks before this many bytes are in + * the send queue, the system will deadlock. + */ + protected static final int MIN_CLIENT_BUFFER = 2 * 32 * 46 + 4; static final String OPTION_INCLUDE_TAG = "include-tag";diff --git a/org.spearce.jgit/src/org/spearce/jgit/transport/TransportLocal.java b/org.spearce.jgit/src/org/spearce/jgit/transport/TransportLocal.java index cffdba1..428f73e 100644 --- a/org.spearce.jgit/src/org/spearce/jgit/transport/TransportLocal.java +++ b/org.spearce.jgit/src/org/spearce/jgit/transport/TransportLocal.java@@ -175,7 +175,7 @@ InternalLocalFetchConnection() throws TransportException { // force the buffer to be big enough, otherwise it // will deadlock both threads. { - buffer = new byte[MAX_CLIENT_BUFFER]; + buffer = new byte[MIN_CLIENT_BUFFER]; } }; out_w = new PipedOutputStream(out_r);-- 1.6.3.48.g99c76